This invention relates to the problem of transfer of solid particles between vessels in situations where there is a temperature differential between the two vessels. More specifically, the invention relates to use of a fluid to suspend the particles in a slurry mixture which will accomplish such transfer causing minimal damage to the particulate transferred substance.
There are a number of industrial processes for which it is desirable to transfer solids from one container to another and simultaneously to effect a temperature increase. Prominent among these processes are catalyzed reactions such as those in the petroleum industry which often involve catalysis of reactions carried out at high temperature. Generally, such catalysts are solids with high surface areas and, although not directly consumed in a catalyzed reaction, become "spent" as the reaction is repeated either through contamination or decomposition. In such cases, it may be desirable to continue to transfer the catalyst into the reactor when the reactor is at high temperature. While it is possible to replace such spent catalyst by dismantling the reactor and replacing the catalyst directly or by using a series of reactors and alternately taking one or more "swing" reactors out of the process stream, then separately and directly replacing or reactivating the catalyst in the swing reactor, a number of continuous catalyst replacement systems have also been devised. In these latter cases, it is inevitable that transfer from a lower to a higher temperature will be required.
All of the above processes fail to address the problem of catalyst breakage. Because the catalyst reservoir containing the fresh or regenerated catalyst is generally at a temperature considerably lower than that at which reaction takes place or even than the temperature of a shut-down reactor, catalyst entering the reactor is exposed to considerable temperature, and, therefore, internal pressure shock.
The catalyst particles, in general, contain the active material on the surface area of a support which is formed from such inert material as aluminum oxide, silica, mixtures of alumina and silica, or Zeolite. The efficiency of the catalyst depends on the high surface area to which such catalytic materials as vanadium, cobalt, molybdenum, nickel, tungsten, and the like (depending on the reaction to be catalyzed) are to be found. Typically, one gram of such catalyst has a surface area of several hundred square meters. In order to achieve this surface area, and still retain practical particle size, the particulate forms of the the catalyst must be extremely porous. Such porosity, however, results in pockets of liquid or vapor within each individual particle which, upon vaporization and/or expansion due to a temperature increase, can, and do, cause serious breakage problems to the catalyst. In short, when the regenerated catalyst is transferred back into the reactor at a high temperature, expansion of fluid in the particle pores causes break-up of the particles so that the resulting fine powders are both difficult to handle and less efficient as catalyst. Of course, the presence of finely divided powdered materials will cause ancillary problems with respect to system blockage and contamination of the reactant stream.
The present invention is directed to utilizing a slurry mixture containing suspended catalyst or other particulate multiple pore solids, such that the mixture can be transferred from a storage tank of a lower temperature to a location of higher temperature, where, in most practical applications, reaction takes place. By use of the slurry mixture of the invention, catalyst particles or other similar particles can be transferred over considerable temperature differentials without breaking, or crumbling so that it is possible to avoid generating the problems that ensue from such breakage.